We are trying to distinguish between Stratified Random Sampling and BlockDesign. BPS makes the point:

"Blocks and strata both group similar units. We use two different namesonly becuase the idea developed separately for sampling and experiments." pg 214

So what is the party line? Are they the same? Is there a difference?

Thanks in advance,

Al

----- End of forwarded message from AlCoons@aol.com -----

I'd say it is the same concept applied to different situations.

Here's another example. When I teach linear models I present analysisof covariance in the following way.

Sometimes we want to study the effect of one or more variables x1,x2, ... on another variable, y. We ALREADY know that y also dependson z1, z2, ..., and if we do not include the z's in the model, we willget a very poor model. So we include the z's to get a good model, andthen test hypotheses about the x's.

Or as Joe Ward would say, "If you can't control for it, measure it."

In the traditional situation, the x's represent cells in an ANOVA andthere is one z and it is a measurement variable. So, is what I doREALLY analysis of covariance? I'd say it is the same idea applied toa broader range of situations. I prefer the broader framework forteaching, and see no reason to say much about the narrower idea.However, if you were going to do a literature search, it might beuseful to know that virtually all of the literature you turned upwould be about the narrower situation.

Similarly, if you are teaching blocking and stratified sampling, Idon't think it is important to draw a distinction. However, if youwant to do a literature search it would be useful to know that thehistory of this basic idea within experimental design has beendifferent than its history within survey sampling, so you might needto search both areas, using the locally accepted terminology in each,if you wanted to research the impact of this basic idea instatistics.

But for purposes of AP Stats., I think what David Moore says isexactly what should be said on this topic (indeed, on MOST topics!).